Vehicle engines may be operated with gaseous fuels as an alternative to liquid fuel. Alternatively, vehicle engines may be operated with a combination of liquid and/or gaseous fuels. Operating an engine with a gaseous fuel may provide owner/operator benefits in the form of lower operating costs and vehicle emissions. For example, starting an engine via combusting a gaseous fuel may reduce engine starting emissions. Further, gaseous fuels such as methane may have cost advantages over liquid fuels such as gasoline.
On the other hand, operating an engine using a gaseous fuel injector may degrade engine air-fuel control during some conditions. For example, when methane is injected into an engine intake manifold or cylinder intake port while air is being drawn into the intake manifold, gaseous fuel can cause air to be displaced from the intake manifold. If the individual amounts of air and gaseous fuel cannot be established, the engine may operate leaner or richer than is desired. Therefore, for the benefits of gaseous fuels to be fully utilized, it may be desirable to accurately determine the amounts of air and gaseous fuel entering engine cylinders.
The inventor herein has recognized the above-mentioned disadvantages and has developed a method for operating an engine, comprising: adjusting an amount of air inducted into an engine in response to output of a temperature sensor in an engine air intake; and adjusting the amount of air inducted into the engine in response to a temperature of a gaseous fuel after expansion of the gaseous fuel, the temperature of the gaseous fuel not based on the temperature sensor.
By adjusting an amount of air inducted into a cylinder responsive to a temperature sensor and a temperature of a gaseous fuel after expansion that is not based on the air temperature sensor, it may be possible to improve engine air-fuel control when an engine air amount is adjusted based on a single temperature sensor. For example, in many gaseous fuel applications, intake manifold temperature is measured at a collector area to provide an average intake manifold temperature. However, gaseous fuel is commonly injected at individual cylinder intake ports to improve transient air-fuel control. As a result, the temperature sensor located at the collector area may not provide an accurate temperature of the air-fuel mixture at the entrance to the cylinder (e.g., the cylinder inlet port). A more accurate air-fuel mixture temperature estimate may be provided by combining knowledge of the air temperature from the upstream air temperature sensor with an estimate of gaseous fuel temperature after the gaseous fuel expands in the air intake. An air-fuel mixture temperature may be determined from the individual streams of gaseous matter: air and gaseous fuel temperatures. In this way, it may be possible to provide a better estimated air-fuel mixture temperature so that the amount of air entering a cylinder may be more accurately determined.
The present description may provide several advantages. In particular, the approach may improve engine air-fuel control. Further, the approach may provide improved air-fuel control without adding system cost.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.